A tune is required for just a TBE, but you will be removing a restriction from the flow of exhaust from the engine, helping it to breathe better and changing the way it works, so it certainly is recommended. But as stated already, the best bang for buck is to collect up a standard set of entry level supporting mods such as the intake and fuel pump, and get it all tuned to work together in one hit so that later on you are prepared to upgrade the turbo or intercoolers with a minimal retune.